1. Field of the Invention
The invention relates to an electronic component with an insulating layer.
Electronic components can include an insulating layer. Insulating layers include plastics in addition to the purely inorganic insulating layers, such as silicon dioxide layers and silicon nitrite layers. In comparison with the inorganic insulating layers, these plastics have the disadvantage of a high relative dielectric constant. Consequently, they may not adequately suppress capacitive coupling effects between conductor tracks and also undesired noise effects and impair the function of electronic components.
2. Summary of the Invention
It is accordingly an object of the invention to provide an electronic component with an insulating layer formed from fluorinated norbornene polymer and a method for manufacturing the insulating layers that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that improves the function of electronic components with at least one insulating layer and provides insulating layers that change the relative dielectric constant to the needs and requirements of the electronic circuit of an electronic component.
With the foregoing and other objects in view, there is provided, in accordance with the invention, an electronic component having an insulating layer. The insulating layer has a polymer including norbornene monomers C7H10. The norbornene monomers have a double ring structure, carbon atoms at second and third positions, and carbon double bonds between the carbon atoms at the second and third positions. The polymer retains the double ring structure of the norbornene monomers by breaking the carbon double bonds between the carbon atoms of the second and third positions and has norbornene monomers crosslinked by homopolymerization with polar fluorocarbon bonds.
With the objects of the invention in view, there is also provided a method of producing an electronic component with an insulating layer having a polymer including norbornene monomers. The method includes partially fluorinating a starting material of a diene synthesis of norbornene monomers. The next step is preparing fluorinated norbornene monomers by diene synthesis from the partly fluorinated starting materials. The next step is homopolymerizing the fluorinated norbornene monomers under increased pressure and at increased temperature by breaking the carbon double bond between the carbon atoms of the second and third positions of the norbornene monomer to form polymer chains. The next step is processing the polymer chains by dissolving the polymer chains in organic solvents to form an insulating layer.
With the objects of the invention in view, there is also provided an additional method of producing an electronic component with an insulating layer having a polymer including norbornene monomers. The method includes preparing norbornene monomers by diene synthesis from cyclopentadiene and ethylene. The next step is fluorinating the norbornene monomers to a degree of fluorination between 10% and 100%. The next step is homopolymerizing the norbornene monomers under increased pressure and at increased temperature by breaking the carbon double bond between the carbon atoms of the second and third positions of the norbornene monomer to form polymer chains. The next step is processing the polymer chains by dissolving the polymer chains in organic solvents to form an insulating layer.
According to the invention, the electronic component with at least one insulating layer has a polymer including norbornene monomers. The polymer in this case retains the double ring structure of the monomer C7H10 while breaking the carbon double bond between the carbon atoms of the second and third positions of the norbornene monomer.
The norbornene monomers crosslinked by homopolymerization have polar fluorocarbon bonds. A plastic having norbornene monomers crosslinked by homopolymerization has the advantage that the relative dielectric constant can be tailored to the needs of electronic components, in particular, the insulating layers of these electronic components. The relative dielectric constant can be varied considerably by fluorination of the norbornene monomer and by homopolymerization crosslinkage to form an insulating layer by the substitution of hydrocarbon bonds by polar fluorocarbon bonds to give a relatively low dielectric constant. With the aid of fluorinated, homopolymerized polymers including norbornene monomers, relative dielectric constants for insulating layers down to the value 2.0 are achievable, and are variable within a low range of the relative dielectric constant between the values 2.0 and 4.0.
To achieve this variation of the dielectric constant, in one embodiment of the invention, the polymer including norbornene monomers has a degree of fluorination obtained by providing polar fluorocarbon bonds instead of hydrocarbon bonds of 10% to 100%. Consequently, at least every tenth hydrocarbon bond has been substituted by a polar fluorocarbon bond up to complete substitution (100%) of the hydrocarbon bonds by fluorocarbon bonds.
By varying fluorination, a variation of the relative dielectric constant for the polymer including norbornene monomers can be achieved. In addition, the adhesiveness of the plastic can be controlled, from a highly tacky composition to a scarcely wetting composition. The interrelationship between tackiness or adhesiveness and degree of fluorination is such that there is still outstanding and intensive adhesiveness at the lower limit of 10% of fluorination, while it is lost almost completely at complete fluorination (100%).
In a polymer including norbornene monomers for insulating layer electronic components, the polymer has a degree of fluorination obtained by providing polar fluorocarbon bonds instead of hydrocarbon bonds of 30% to 75%. At 30%, outstanding adhesive behavior is still ensured for this substance, but a reduced relative dielectric constant is already achievable. This dielectric constant is further reduced as the degree of fluorination increases up to 75%, and simultaneously the adhesive properties diminish. However, at a degree of fluorination of 75%, the adhesiveness of the plastic to inorganic protective and passivation layers of silicon dioxide and/or silicon nitrite and to the exposed metal surfaces is still intensive enough for it to be used for electronic components without having to introduce an adhesion-promoting layer between the inorganic layers or metal layers of a semiconductor chip and the insulating layers according to the invention.
A further embodiment of the invention provides that the polymer including norbornene monomers has a degree of fluorination obtained by providing polar fluorocarbon bonds instead of hydrocarbon bonds of 50% to 70%. This narrow band for the degree of fluorination can be achieved by suitable mixing of correspondingly pre-fluorinated norbornene monomers and subsequent homopolymerization to form crosslinked norbornene monomers. In this case, both the reduction of the relative dielectric constant and the adhesive effect of an insulating layer of a fluorinated polymer including norbornene monomers lie in a range that is of advantage for insulating layers in electronic components. Consequently, the relative dielectric constant can be reduced in stages by the gradual fluorination of the polynorbornene.
With the degree of fluorination of this embodiment, a relative dielectric constant can be covered by the dipole effect of the polar fluorocarbon bond down to the value 2.0 and combined with a required adhesive force, and optimized. In this case, the degree and position of the fluorination are decisive for adapting the desired property of a low relative dielectric constant and a simultaneously high adhesion for the needs of an insulating layer in an electronic component.
In a further embodiment of the invention, it is therefore provided for five to seven positions out of ten possible positions in the norbornene monomer for hydrogen atoms to be occupied by fluorine atoms and for the remaining three to five positions to be occupied by hydrogen atoms. At 60%, this degree of fluorination lies in the range of the last embodiment of the invention between 50% and 70%.
A further embodiment of the invention provides that at least the two carbon bonds of the seventh position in the norbornene monomer are substituted by polar fluorocarbon bonds. In the case of the previous embodiments, it was a matter of adapting the degree of fluorination to the needs of electronic components by making the sum of the fluorocarbon bonds and the sum of the hydrocarbon bonds lie within a fixed bandwidth. In the case of this further embodiment, it is a matter of defining the position of the fluorination within the double ring structure of the monomer. In this case, the seventh positions of the hydrocarbon bonds of the norbornene monomer are to be substituted by polar fluorocarbon bonds. The seventh position of the double ring structure of the norbornene monomer is an exposed stable position that is retained unchanged in the homopolymerization. It is not varied or changed during the polymerization like the positions two and three, which serve for the chain formation by breaking their double bond.
A further embodiment of the invention provides that six fluorine atoms are disposed on the first, second, third, fourth, and seventh positions and four hydrogen atoms occupy the fifth and sixth positions. In a way similar to the seventh position, the fifth and sixth positions within the double ring structure of the norbornene monomer are exposed positions that are not involved in the homopolymerization phase. Norbornene monomers of this type allow a fluorination of 60% to be achieved because six fluorine atoms occupy the norbornene double ring.
In a further embodiment of the invention, eight fluorine atoms occupy the first, fourth, fifth, sixth, and seventh positions of the norbornene double ring and only two hydrogen atoms occupy the second and third positions. This embodiment corresponds to a degree of fluorination of 80%, which consequently lies above the 70% and 75% of the previous embodiments. However, by mixing norbornene monomers in which the first, second, third, fourth and seventh positions are occupied by fluorine atoms with norbornene monomers in which the first, fourth, fifth, sixth, and seventh positions are occupied by fluorine atoms, any desired degree of fluorination between 60% and 80% can be set.
In a further embodiment of the invention, a plastic polymerized in this way is used as an insulating layer. In a further embodiment of the invention, norbornene-based plastic insulating layers of this type are used in electronic components for wiring planes and insulate wiring lines from the conductor tracks, which are disposed directly on a semiconductor chip. However, a polymer including norbornene monomers can also take the form of an insulating film, which by coating with a structured metal layer can likewise be used for a wiring film in electronic components. In particular in the case of the wiring films, a low relative dielectric constant is of great importance because two conductor track systems lie one above the other separated only by the insulating film that is on the one hand the conductor track system of the active upper side of the semiconductor chip and, on the other side of the insulating layer, the structured metallization for a wiring plane. A minimized relative dielectric constant consequently allows improved decoupling and an improved signal-to-noise ratio to be achieved for the electronic component. Crosstalk or other coupling effects can also be minimized in this way.
In a further embodiment of the invention, a wiring layer or wiring film may be disposed directly on a semiconductor wafer. The wiring film or the wiring layer on the semiconductor wafer has wiring lines. These wiring lines connect contact areas on the active upper side of the semiconductor wafer to external contacts on the wiring layer or wiring film of the electronic component. Polymers including norbornene monomers are ideally suited for providing an insulating layer on complete semiconductor wafers, which are the starting product for a number of electronic components. After subsequent metallization and forming of a wiring structure, the semiconductor wafer can be sawn up to produce electronic components. After the sawing, each component carries a wiring film including a polymer of the norbornene monomer.
On the other hand, in a further embodiment of the invention it is possible to provide each individual semiconductor chip that has been cut out from a semiconductor wafer with a wiring layer or a wiring film including a polymer of the norbornene monomer on its active upper side. If a wiring film is included, it can be adhesively bonded onto the semiconductor chip, while a screen printing method may be carried out for applying a wiring layer. The wiring conductor tracks in this case connect contact areas on the active upper side of a semiconductor chip to external contacts on the wiring layer or wiring film.
In a further embodiment of the invention, the wiring film has a plurality of layers of wiring conductor tracks including a metal and insulating layers containing a polymer of the norbornene monomer. These multiple wiring films are required whenever the wiring conductor tracks have to be packed so densely that crossunders and crossovers of wiring conductor tracks become necessary. For this purpose, a contact via is produced through the insulating layer including a polymer of the norbornene monomer to the wiring conductor tracks lying thereunder.
In the case of a further embodiment of the invention, it is provided that the relative dielectric constant of the insulating layer including a polymer of the norbornene monomers has a value between 2.0 and 2.4. That is a significant improvement in comparison with polyimides and other insulating layers because a value for the relative dielectric constant in the range from 2.0 to 2.4 is not achievable with polyimide or comparable materials.
A method of producing an electronic component with at least one insulating layer, the insulating layer having a polymer including norbornene monomers, has the following method steps:                fluorination of at least one of the starting products of the synthesis of norbornene monomers,        preparation of the fluorinated norbornene monomer by diene synthesis from the fluorinated starting products,        homopolymerization of the fluorinated norbornene monomers under increased pressure and at increased temperature and breaking of the carbon double bond between the carbon atoms of the second and third positions (2, 3) of the norbornene monomer to form polymer chains,        processing of the polymer by utilizing its ready solubility in organic solvents to form at least one insulating layer of an electronic component.        
This method has the advantage that, by fluorinating the norbornene monomer in a range of the degree of fluorination from 10% to 100%, on the one hand a very low relative dielectric constant can be achieved, provided that the degree of fluorination is increased to around 100%. At the same time, the adhesiveness of the plastic on inorganic substances such as silicon dioxide or silicon nitrite and also on metal can be adapted to the needs for electronic components, provided that the degree of fluorination is kept as low as possible. An optimum degree of fluorination for many applications therefore lies between 50% and 70%.
The ready solubility of the polymer in organic solvents can be used for processing the polymer to form films or deposited layers. In that, the polymer including fluorinated norbornene monomers is diluted with organic solvents in order to transform it into films by vaporizing the solvents. Consequently, very thin deposited layers in a thickness of a few micrometers, preferably 0.3 to 3 μm, can be achieved. In an example of how the method is conducted, the diluted polymer is applied to a semiconductor wafer by spin-coating or it is brought onto the semiconductor wafer by the immersion method.
An alternative method of producing an electronic component with at least one insulating layer, the insulating layer having a polymer including norbornene monomers, has the following method steps:                preparation of the norbornene monomer by diene synthesis from cyclopentadiene and ethylene C2H4,        fluorination of the norbornene polymer to a degree of fluorination between 10% and 100%,        homopolymerization of the norbornene monomers under increased pressure and at increased temperature and breaking of the carbon double bond between the carbon atoms of the second and third positions (2, 3) of the norbornene monomer to form polymer chains,        processing of the polymer by utilizing its ready solubility in organic solvents to form at least one insulating layer of an electronic component.        
In the case of this method, including a fluorination of the norbornene monomer, after its synthesis from cyclopentadiene and ethylene, the reference to a positional determination of the fluorine atoms in the monomer is slightly restricted in comparison with the above method. However, this has the advantage that the user can use synthesized norbornene monomers as a starting product in the fluorination.
The method of producing an electronic component may, furthermore, have the following method steps:                coating of the insulating layer including a polymer of norbornene monomers with a metal layer,        structuring of the metal layer to form wiring conductor tracks with contact terminal areas at one end of the wiring conductor tracks on the insulating layer, and        structuring of the insulating layer by opening at least one bonding channel, in which contact areas of an active upper side of a semiconductor chip are exposed.        
With this method, an insulating layer for wiring conductor tracks is created in the semiconductor component. This overcomes the disadvantages of previous plastic insulating layers, with an extremely low relative dielectric constant. Improved decoupling of the signal transmission in the structured metal layer on the insulating layer including polymer of norbornene monomers and the structured metal layer on the semiconductor chip is achieved. The structured metal layer on the semiconductor chip has on its active upper side metallic and polysilicon conductor tracks, to connect electrodes of active and passive components of an integrated circuit to corresponding metallic contact areas on the semiconductor chips. The lower a relative dielectric constant can be made for a polymer layer of norbornene monomers of this type, the thinner the insulating layers can be applied, and consequently at the same time a reduction in the spatial expanse can be achieved in an advantageous way for the electronic component.
As already mentioned above, the use of appropriate organic solvents in which the polymer of norbornene monomers is readily soluble allows the insulating layer of a wiring layer to be applied directly to a semiconductor wafer by spraying and/or spin-coating. This has the advantage that a plurality of semiconductor chips can be coated with the insulating layer including a polymer of norbornene monomers simultaneously in a single processing step.
In a further example of how the method is conducted, a polymer layer of norbornene monomers can also be applied directly to a semiconductor wafer by the semiconductor wafer being immersed in an organic solution with dissolved polymer. An immersion method of this type has the advantage that, with an appropriate holding fixture, several hundred semiconductor wafers can be coated with a polymer layer of norbornene monomers at the same time.
After vaporizing of the solvent, a thin, and, if required, fine polymer layer of a thickness in the submicrometer range remains on the wafer, which then has to be provided with a structured metal layer as a wiring plane. A structured metal layer of this type can be applied by a printing technique and/or by physical depositing of the metal from the vapor phase onto the surface of the insulating layer. In the case of physical deposition, it is possible with one method step for a plurality of semiconductor wafers to be simultaneously coated with a metal layer, which is then subsequently structured by appropriate photolithography steps.
However, the polymer including norbornene monomers may also be used for a multi-ply layer including insulating layers and interposed wiring conductor tracks of structured metal layers. For this purpose, contact vias that connect the individual structured metal layers under one another or over one another are made in the insulating layers including a polymer of norbornene monomers.
In the case of a further example of how the method is completed, a structured insulating layer including a polymer of norbornene monomers is applied as a solder resist layer to the wiring layer with a structured metal layer. In this embodiment of the method, the wiring lines are protected against corrosion and against spreading of solder material by the polymer layer including norbornene monomers, which is used as a solder resist layer. Only the contact terminal areas of the wiring layer remain freely accessible. Contact terminals, for example solder balls, are subsequently applied to these freely accessible contact terminal areas of the wiring layer. This polymer layer including norbornene monomers then serves simultaneously as a package outer side of the semiconductor component.
Because the above method steps can be conducted both on an individually separated semiconductor chip and on a semiconductor wafer for a plurality of semiconductor chips, for the production of electronic components from a semiconductor wafer it is necessary for the latter finally to be separated into individual components.
These components may then be delivered directly to the customer or additionally coated on the rear side or on the edge sides with a plastics composition.
In a further example of how the method is conducted, the encapsulation with a plastics composition is completed before the contact terminals are applied to the contact terminal areas because the semiconductor chip with contact terminal areas but without a contact terminal represents a relatively planar supporting surface during the injection-molding of the rear side of the semiconductor chip and the edge regions of the semiconductor chip. Consequently, in the case of this method, the contact terminals are only applied, for example, by a process involving soldering solder balls on the contact terminal areas, after the semiconductor chip has been provided with a plastic package on the rear side and the edge sides.
To summarize, this results in the insulating layer according to the invention including a polymer of norbornene monomers and wiring planes with polymer layers that have a low relative dielectric constant. Although relative dielectric constants with values below 2 can be achieved with pure polytetrafluoroethylene such as that sold under the trademark TEFLON®. However, polytetrafluoroethylene is unsuitable as an insulating layer for use in electronic components because of its poor adhesion properties. Polytetrafluroethylene is unsuitable because polytetrafluoroethylene is known as a nonstick agent and consequently cannot be used directly as an adhering insulating layer in electronic components. Materials with good adhesion, such as polyimide or polybenzoxazole (PBO), however, lie with their relative dielectric constants of around 4 in a range that is accompanied by signal coupling problems and noise problems. By the gradual fluorination of polynorbornene, the value of the relative dielectric constant can be reduced in stages. The degree of fluorination allows coverage of a range for the relative dielectric constant that can also cover the part of technical interest, down to below 2.0, on account of the dipole effect of the polar fluorocarbon bonds. This property can be optimized in combination with the required adhesive force for insulating layers in an electronic component. The degree and position of the fluorination allows the desired property, that is, a low dielectric constant or improved adhesion, to be adapted in the application concerned.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an electronic component with at least one insulating layer, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.